SECURITIES - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Investments, Debt and Equity Securities [Abstract]
Residential investment securities sold, carrying value	$ 25,500.0	$ 45,600.0	$ 12,900.0
Residential investment securities sold, net realized gain (loss)	$ (37.8)	$ (1,100.0)	$ (6.4)